PARIS -- A study on serum samples of over 9,000 French adults suggests that COVID-19 infection may have occurred as early as November 2019 in France as some sampled between November 2019 and January 2020 tested positive for antibodies against the virus.

The research, led by Fabrice Carrat, director of Pierre Louis Institute of Epidemiology and Public Health, was published in the European Journal of Epidemiology on Feb. 6.

All 9,144 serum samples were collected between Nov 4, 2019 and March 16, 2020 from participants living in the 12 mainland French regions. Their average age is 55 and 51 percent of them are female, said the report.

"We identified 353 participants with a positive anti-SARS-CoV-2 IgG test," and "neutralizing antibodies were detected in 44 participants," it said.

Strikingly, 13 participants with positive IgG and neutralizing antibodies were sampled between Nov 5, 2019 and Jan 30, 2020, seven of whom had their serum sample collected in November 2019. Researchers believe that this study suggests COVID-19 presence in France as early as November 2019.

On May 7, 2020, Albert Schweitzer hospital in Colmar, East France, announced in a press release that their radiologists reviewed 2,456 chest scans performed between Nov 1, 2019 and April 30, 2020, with results showing that the first suspected case dated back to Nov 16, 2019.

On May 3, 2020, Yves Cohen, head of the intensive care units of two hospitals affiliated to AP-HP, told French media that the hospitals re-examined samples taken from 24 pneumonia patients between December 2019 and January 2020. Results showed that a man, who was admitted to hospital on Dec 27, 2019 and now in good health, tested positive for COVID-19.